The latest House Condition Survey report has found about half of all houses lacked adequate insulation (47 per cent), contributing to many being damp and mouldy (49 per cent).
It looked at 560 houses nationwide and weighted findings to represent the total number in New Zealand.
In 46 per cent of homes, bedrooms were unheated and five per cent of homes were not heated at all.
These findings come as part of the largest survey of its kind – the Building Research Association of New Zealand (BRANZ) report into the state of our homes – done every five years since 1994.
The Branz report found dampness and mould were more prevalent in rental homes, with 56 per cent of these showing mould – compared to 44 per cent of owner-occupied homes.
Mould was most common in bathrooms, and in 20 per cent of living areas and bedrooms.
In rentals the situation was worse – almost 30 per cent had visible mould in bedrooms, compared to 18 per cent in owner-occupied houses.
Many renters (38 per cent) also did not have access to cost-effective heating appliances, such as heat pumps, wood burners, and flued gas heaters, compared to just 12 per cent of homeowners who went without.